Projectile propelled by friction drag of high velocity plasma



Aug. 15, 1967 F. E. NULL ET AL 3,335,637

PROJECTILE PROPELLED BY FRICTION DRAG OF HIGH VELOCITY PLASMA Filed Dec. 23, 1965 2 Sheets-Sheet 1 RAYMOND A. VER/V/Ll/O/V Aug. 15, 1967 2 Sheets-Sheet Filed Dec. 23, 1965 ma mw qlv W i MV%%7 Z A V 6 United States Patent 3,335,637 PROJECTILE PROPELLED BY FRICTION DRAG OF HIGH VELOCITY PLASMA Fay E. Null, Shalimar, and Raymond K. Vermillion, Valparaiso, Fla., assignors to the United States of America as represented by the Secretary of the Air Force Filed Dec. 23, 1965, Ser. No. 516,168 8 Claims. (Cl. 89-1) ABSTRACT OF THE DISCLOSURE An hydrodynamic nozzle for furnishing a long, high density column of plasma in parallel flow to a launch tube which has a projectile containing section and a collimating section at its upstream end. The projectile is of the built-up type of very thin walls and small angle front edges to allow for propulsion by friction drag rather than pressure drag.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to use of any royalty thereon.

This invention relates generally to hypervelocity weapons, and more particularly, to a launch tube and projectile which utilizes the friction drag of high velocity plasma as the propelling force.

Hypervelocity weapons are required for satellite offense and defense in order to provide for reduced lead angle in order to destroy an enemy vehicle prior to its having fired a lethal shot. High energy plasmoids have been proposed for use as a projectile, however, by the time it reaches a long range target its volume is increased and its density decreased, thereby rendering it ineffective for this purpose.

Plasma may be utilized, however, to couple kinetic energy of a plasma to a projectile by either pressure drag, friction drag or both. Within the realm of practical plasma masses it was found that spherical projectiles were unable to be made of a size sufficiently large to provide the necessary penetration through the skin of a satellite vehicle. Rod type projectiles usually have too much mass relative to their surface area to attain the higher supersonic velocities.

Accordingly, this invention utilizes a long high density column of plasma in parallel flow to cause the propelling of a projectile by friction drag. The projectile is a thin walled structure of the built-up type with a large surface area for the drag acceleration together with a relatively low mass. Since the thin walls have the same high density per unit cross section area as a rod, it produces superior penetration of the target.

It is a primary object of this invention to produce a plasma propelled, hypervelocity projectile wherein the projectile ispropelled by a high density column of plasma in parallel flow.

It is another object of this invention to provide a projectile capable of being propelled by a plasma wherein the projectile has very thin walls and small angled front edges in order to assure its being propelled by friction drag rather than pressure drag.

It is still another object of this invention to provide a plasma propelled projectile capable of attaining hypervelocities wherein the spacing between the walls of the projectile prevents overlap of boundary layers.

It is a further object of this invention to provide a launch tube for a plasma propelled, hypervelocity projectile for alignment of the projectile while the plasma flows through and around it.

It is a still further object of this invention to provide a launch tube for a plasma propelled, hypervelocity pro- Ice jectile wherein the launch tube includes collimating vanes upstream of the projectile to prevent lateral forces caused by any residual angle of incidence in the plasma fiow.

Another object of this invention involves a plasma propelled, hypervelocity projectile with spin-up vanes thereon to maintain projectile orientation after projectile launch.

Still another object of this invention involves the provision of a plasma propelled, hypervelocity projectile which is long when compared with its thickness so as to have a large mass density per unit of impact area in order to provide relatively great penetration of a target.

A further object of this invention involves the provision of a high density column of plasma in parallel flow by means of a magnetic or hydrodynamic nozzle in order to propel a hypervelocity projectile.

A still further object of this invention involves the production of a plasma propelled, hypervelocity projectile of fused quartz that does not absorb the incident radiation from the boundary layers of the plasma and which gives ablation protection against heat transferred from the turbulent boundary layer.

Still another object of this invention involves the proviison of a combination arrangement for producing a long, highdensity column of plasma with a launch tube and a hypervelocity projectile which are easy and economical to produce of standard, conventional materials that lend themselves to standard mass production manufacturing techniques.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings, wherein:

FIGURE 1 is an isometric view of the built-up projec tile of this invention;

FIGURES 1A and 1B are representations of the diflerent types of leading edges utilized on the projectile of FIGURE 1 in order to assure propelling of the projectile by frictional drag;

FIGURE 2 is a view in cross section of the launch tube of this invention with a schematic representation of the propelling plasma generation means; and

FIGURE 3 is an end view taken on lines III-Ill of the launch tube illustrating the vertical collimating vanes.

FIGURE 1 illustrates the main features of the projectile 10. It consists essentially of concentric cylinders 12 and 14 positioned by interior bracing 16 and 18 and skewed spin-up blades 20. The material forming the projectile is fused quartz because of its strength, low density, and a high heat of ablation. With a plasma temperature of 10,000 K. and a Mach No. of 42, the boundary layer temperature would cause 'less than 10% ablation when quartz is utilized. The walls are all of the same thickness, 0.0005 inch, so that each unit area of surface, will for the same drag force have the same mass, and hence, the same acceleration, and for symmetrical flow there will be no forces between different sections of the projectile. The cylindrical shape gives a large concentration of mass per unit of impact area, with deep penetration, while spin-up during launch caused by the skewed blades 20 provides gyroscopic stabilization for end-on impact.

A number of techniques might be employed for construction of the projectile 10; however, the thickness of the parts is probably too small for die casting methods unless provision is made for heating the die. A thermocouple type technique is applicable since a plasma arc spray has been proven as a method for depositing thin layers of metal or refractory oxide with uniform thickness. Layers deposited on a metal substrate could be flame flowed to give a high strength to the quartz layer. The metal substrate could then be removed by flaming in an oxidizing atmosphere. Thus, layers of fused quartz forming the interior bracing 16 could be plasma sprayed on 3 metal backing of the shape of each brace 16. The quartz surfaces could then be aligned, as shown, and a traveling spot flame at the junction of the two elements 16 could fuse the joint. The metal backing could then be removed either by acid or flaming in oxygen.

A metal foil cylinder could be sprayed on its outer surface with quartz to form the cylinder 12. The quartz bracing 16 would then be inserted in the quartz cylinder 12 and a traveling flame utilized to fuse the quartz bracing 16 to the quartz cylinder 12; the metal foil being then burned off. Metal foil ribs with quartz layers would be positioned in a jig for application of a quartz fillet by fire flame to fuse the ribs 18 to the outer surface layer of quartz cylinder 12. The outer quartz cylinder 14 is sprayed on the interior of a metal foil tube in a similar manner and the quartz ribs 18 are then sealed to the interior of quartz cylinder 14; the outer foil layer being burned off. The skewed spin-up vanes 20 consist of L-shaped metal strip positioned on the outer portion of cylinder 14 by jigs, with a quartz layer sprayed on the radial side. The quartz layer would fuse to cylinder 14 by a traveling flame; the L-shaped metal surface then being burned away.

Referring to FIGURES 1A and 1B, there is shown various arrangements by which a sharp edge at the forward end of the projectile is realized. Since the projectile has a length large compared to its thickness, it cannot be efiiciently accelerated by pressure drag from one end by virtue of the fact that the shock produced by a plasma with a very high Mach number exceeds the compressive strength of known materials. Accordingly, friction drag is utilized in this invention since it has the advantage that no part of the projectile needs to push or pull on another. Each unit area of wall surface receives the same acceleration since the friction drag per unit area can be made the same and the mass per unit surface area is constant for the same thickness. Turbulent flow would be present except for a short length at the extreme front edge and turbulence can also be established here by the use of a trip calibrated roughness on the front edge. By grinding a small angle bevel as shown in FIGURES 1A and 1B on the forward portions of the thin walls, oblique shocks from the front edge can be kept to a minimum. With these conditions the projectile may be made any diameter and length without changing the acceleration providing the wall thickness is kept constant. The dimensions of the projectile, therefore, are limited only by the size and energy of the driving plasma required.

A sample set of parameters for the projectile 10 would include:

Size: 0.31 inch diameter x inches long; Weight: 1.87 X slugs;

Velocity: 117,000 feet per second; and Penetration: over 2.58 inches of steel.

The plasma supply is obtained from a conventional magnetic nozzle schematically indicated at the left of FIGURE 2. The plasma stream may be of relatively short length since the acceleration period for the projectile is required to last for only a few hundred thousandths of a second. The boundary layer, during this time, does not have sufiicient time to grow to the steady state value. Drag acceleration is, therefore, relatively large and allows for hypervelocity conditions with a minimum plasma length.

Requirements for the plasma would be:

Size: 0.5 inch diameter x 10 feet long;

Density: atmospheric 7.65 X 10 lbs. per cubic foot; Temperature: l0,000 K.;

Velocity: 10 cm./sec.; and

Flow: parallel as from a magnetic nozzle.

In order to obtain the necessary high velocity for the projectile it is made with very thin walls and, accordingly, can not withstand large asymmetrical forces such as those resulting from a poorly collimated plasma flow. Parallel plasma flow, therefore, is a necessity.

The launching tube 24 is composed of an outer wall section 26 and at its downstream end an inner wall section 27. The downstream end is tapered for joinder with a conventional hydrodynamic or magnetic nozzle. The upstream end of launching tube 24 contains sets of collimating vanes to assure parallel flow for avoidance of the aforementioned asymmetrical forces. A series of horizontal vanes 28 and a series of vertical vanes 30 (FIGURE 3) perform the collimating function. Since parallel flows at different velocity do not exist in general without turbulence, it is expected that turbulent mixing would be complete by the time the plasma flow reaches a point proximate to the downstream ends of the vanes 28. The ends therefore would act as an exhaust nozzle with the flow expanding at the tapered portions of the downstream ends of horizontal collimating vanes 28 causing the shock waves to assure that the flow is parallel to the axes of the vanes 28 and the confining walls formed by the launch tube section 27. By rendering the fiow exactly parallel no lateral forces would be produced on the projectile 10, shown in phantom, which would be located in the round bore of the launch tube downstream from the collimating vanes.

Since the collimating vanes are short (0.4 inch long) compared with the projectile, plasma velocity would be reduced by approximately 8.9%. The vane walls have a thickness of about 0.02 inch and with the plasma characteristics stipulated would result in a temperature rise of approximately 508' C. by passage of the plasma.

Shear stress, temperature characteristics and structural the tolerance of conventional, currently available high grade alloy steel.

Upon emanating from the vanes 28 the plasma reaches the circular bore section 32 of the launch tube 24 which contains the projectile 10. In order to achieve spin-up of the projectile the surface vanes 20 (FIGURE 1) were skewed at a slight angle to the longitudinal axis. If the projectile and launch tube were dimensionally and geometrically perfect, spin-up could be avoided because the projectile would maintain its orientation in the vacuum path to the target; however, small asymmetries in turbulent fiow may cause the projectile to oscillate and leave the launch tube with an appreciable end over end rotational velocity.

The angle of skew of the spin-up vanes 20 may be as small as 1.3 in order to reach an angular rotational velocity of 5.98 X 10 radians per second in the period for acceleration, which is 3.96 X10 seconds. The forces on the projectile incurred because of the rotation are easily tolerated by the quartz material utilized in the construction of the projectile.

Thus, there has been described a system whereby plasma from a magnetic or hydrodynamic nozzle is collimated by means of a series of vanes in a launching tube and then passed by and through a projectile in the bore of the launch tube to cause it to be propelled and accelerated by means of friction drag acceleration of the plasma.

A system of this type is capable of projecting projectiles with a velocity in the vicinity of 117,000 feet per second such that, with the use of thin wall projectiles, a cookie cutter type of penetration of over 2.58 inches of steel would be possible.

Although the invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.

We claim:

1. In a plasma propelled, hypervelocity projectile, the combination of a long, high density column of plasma in parallel flow, a projectile having an opening therethrough and comprised of very thin walls with small angle front edges so as to be propelled by friction drag rather than pressure drag by said column of plasma, the spacing a, a... .mam... a...

between walls of said projectile preventing overlap of boundary layers, a launch tube that aligns said projectile while the plasma flows through and around it, and collimating vanes in said launch tube upstream of said projectile to prevent crushing lateral forces due to any residual angle of incidence in said plasma flow.

2. In a plasma propelled, hypervelocity projectile, the combination of a magnetic nozzle to furnish a long, high density column of plasma in parallel flow, a projectile with very thin walls and small angle front edges so as to be propelled by friction drag rather than pressure drag thus preventing plasma impact from breaking up very light walls that can be accelerated to high velocity, the spacing between said walls being arranged to prevent overlap of boundary layers with subsequent reduction in the acceleratiton produced by drag forces, a launch tube that aligns said projectile while the plasma flows through and around it, collimating vanes in said launch tube upstream of said projectile to prevent crushing lateral forces due to any residual angle of incidence in said plasma flow, spin-up vanes on said projectile that maintain projectile orientation after it leaves said launcher, and construction members of said projectile that are long compared with their thickness so as to have a large mass density per unit of impact area and a relatively great penetration.

3-. In a plasma propelled, hypervelocity projectile, the combination of a hydrodynamic nozzle to furnish a long, high density column of plasma in parallel flow, a projectile with very thin walls and small angle front edges so as to be propelled by friction drag rather than pressure drag thus preventing plasma impact from breaking up very light walls that can be accelerated to high velocity, the spacing between said walls being arranged to prevent overlap of boundary layers with subsequent reduction in the acceleration produced by drag forces, a launch tube that aligns said projectile while the plasma flows through and around it, collimating vanes in said launch tube upstream of said projectile to prevent crushing lateral forces due to any residual angle of incidence in said plasma flow, spin-up vanes on said projectile that maintain projectile orientation after it leaves said launcher,

and construction members of said projectile that are long compared with their thickness so as to have a large mass density per unit of impact are and a relatively great penetration.

4. A plasma propelled, hypervelocity projectile comprising a pair of very thin, concentric cylindrical members, longitudinally oriented members between said cylindrical members and within the interior of the inner of said pair of concentric cylindrical members, and skewed spin-up vanes on the outer periphery of the outer of said pair of concentric cylindrical members, the said members being long compared with their thickness so as to have a large mass density per unit of impact area for great penetration.

5. A plasma propelled, hypervelocity projectile as definet in claim 4 wherein the material of said members is quartz.

6. A plasma propelled, hypervelocity projectile as defined in claim 4 wherein the front edges of said members have a small angled bevel.

7. A launch tube for a hypervelocity, plasma propelled projectile comprising a cylindrically bored section for aligning a projectile to be propelled by a long, high density column of plasma, and a collimating section upstream of said cylindrically bored section, said collimating section having a series of horizontal vanes and a series of vertical vanes for collimating plasma flowing through said sections into flow parallel to the axis of said launch tube.

8. A launch tube as defined in claim 7 including means at the upstream end of said launch tube for engagement with a source of high density plasma flow.

References Cited UNITED STATES PATENTS 16,076 11/ 1856 Taggart 2443i23 1,288,883 12/1918 Harvey 244-323 2,559,955 7/1951 Hartwell 2443.23 3,015,991 1/1962 Forbes 10293 X SAMUl I L W. ENGLE, Primary Examiner. 

1. IN A PLASMA PROPELLED, HYPERVELOCITY PROJECTILE, THE COMBINATION OF A LONG, HIGH DENSITY COLUMN OF PLASMA IN PARALLEL FLOW, A PROJECTILE HAVING AN OPENING THERETHROUGH AND COMPRISED OF VERY THIN WALLS WITH SMALL ANGLE FRONT EDGES SO AS TO BE PROPELLED BY FRICTION DRAG RATHER THAN PRESSURE DRAG BY SAID COLUMN OF PLASMA, THE SPACING BETWEEN WALLS OF SAID PROJECTILE PREVENTING OVERLAP OF BOUNDARY LAYERS, A LAUNCH TUBE THAT ALIGNS SAID PROJECTILE WHILE THE PLASMA FLOWS THROUGH AND AROUND IT, AND COLLIMATING VANES IN SAID LAUNCH TUBE UPSTREAM OF SAID PROJECTILE TO PREVENT CRUSHING LATERAL FORCES DUE TO ANY RESIDUAL ANGLE OF INCIDENCE IN SAID PLASMA FLOW. 